The field of the present invention pertains to semiconductor fabrication processing. More particularly, the present invention relates to a device for more efficiently polishing and planarizing a semiconductor wafer.
Electronic systems and circuits have made a significant contribution towards the advancement of modem society and are utilized in a number of applications to achieve advantageous results. Numerous electronic technologies such as digital computers, calculators, audio devices, video equipment, and telephone systems include processors that have facilitated increased productivity and reduced costs in analyzing and communicating data, ideas and trends in most areas of business, science, education and entertainment. Frequently, electronic systems designed to provide these results include integrated circuits (ICs) on chip wafers. Usually, the wafers are produced by processes that include a polishing step to create a smooth wafer surface. Performing the polishing step in an effective and efficient manner is critical to IC wafer manufacturing.
The starting material for typical ICs is very high purity silicon. The pure silicon material is grown as a single crystal that takes the shape of a solid cylinder. This crystal is then sawed (like a loaf of bread) to produce wafers upon which electronic components are then constructed by adding multiple layers to the wafer through a process of lithography (e.g., photolithography, X-ray lithography, etc.). Typically, lithography is utilized to form electronic components comprising regions of different electrical characteristics added to the wafer layers. Complex ICs can often have many different built up layers, with each layer being stacked on top of the previous layer and comprising multiple components with a variety of interconnections. The resulting surface topography of these complex IC""s are bumpy (e.g., they often resemble rough terrestrial xe2x80x9cmountain rangesxe2x80x9d with many rises or xe2x80x9chillsxe2x80x9d and dips or xe2x80x9cvalleysxe2x80x9d) after the IC components are built up in layers.
Lithographic techniques are usually able to reproduce very fine surface geometries and greater advantages and usefulness are realized in applications in which more components (e.g., resistors, diodes, transistors, etc.) are integrated into an underlying chip or IC. The primary manner of incorporating more components in a chip is to make each component smaller. In a photolithographic process, limitations on the depth of focus impact the projection of increasingly finer images onto the surface of the photosensitive layer. Depth of focus problems are exacerbated by rough topographies (e.g., the bumpy rises and dips causes by layers produced during lithographic processes). The xe2x80x9cbumpyxe2x80x9d topography of complex ICs exaggerate the effects of narrowing limits on the depth of focus which in turn limits the number of components that are incorporated on a chip. Thus, in order to focus desirable mask images defining sub-micron geometries onto each of the intermediate photosensitive layers in a manner that achieves the greatest number of components on a single wafer, a precisely flat surface is desired. The precisely flat or fully planarized surface facilitates extremely small depths of focus operations, and in turn, facilitates the definition and subsequent fabrication of extremely small components.
Polishing is the preferred method of obtaining full planarization of a wafer layer. It usually involves removing a sacrificial portion of material by rubbing a polishing pad on the surface of the wafer. Polishing flattens out height differences on the surface of the wafer, since high areas of topography (hills) are removed faster than areas of low topography (valleys). Most polishing techniques have the rare capability of smoothing out topography over millimeter scale planarization distances leading to maximum angles of much less than one degree after polishing.
One of the most common polishing techniques includes chemical mechanical polishing (CMP) processes that utilize an abrasive slurry dispensed on a polishing pad to aid in the smooth and predictable planarization of a wafer. The planarizing attributes of the slurry are typically comprised of an abrasive frictional component and a chemical reaction component. The abrasive frictional component is due to abrasive particles suspended in the slurry. The abrasive particles add to the abrasive characteristics of the polishing pad as it exerts frictional contact with the surface of the wafer. The chemical reaction component is attributable to polishing agents which chemically interact with the material of the wafer layer. The polishing agents soften or dissolve the surface of the wafer layer to be polished by chemically reacting with it. Together the abrasive frictional component and a chemical reaction component assist a polishing pad to remove material from the surface of the wafer.
The manner in which the slurry is distributed to the polishing pad significantly impacts the effectiveness of the abrasive and chemical characteristics of the slurry in aiding the polishing, which in turn impacts the removal rates. The traditional slurry distribution method is to dispense the slurry onto the top of a polishing pad, and the polishing pad transports it to the wafer surface. A polishing pad material usually has a roughened surface comprising a number of very small pits and gouges manufactured into the surface of the polishing pad. The pits and grooves of the roughened surface act as pockets that collect slurry for transportation to and from the wafer surface being polished. While abrasive slurries utilized in typical chemical mechanical polishing processes offer certain benefits, they can also result in detrimental side affects.
The free floating abrasive particles in typical abrasive slurries often pose certain problems. One problem with typical abrasive CMP slurries is uneven polishing as a result of insufficient dispersion stability in most slurries. It is important to evenly distribute the slurry over the surface of the pad and wafer so that the removal of the wafer layer is even. Solid abrasion particles in most slurries tend to settle down and/or aggregate in the slurry solution. If a portion of the wafer is exposed to contact with an excessive amount of slurry it usually is removed at a faster rate and portions that are not exposed to enough slurry are usually removed at a slower rate, creating a rough topography instead of a planarized one. Thus, it is preferable to avoid detrimental uneven layer removal due to agglomeration of the slurry particles and/or non-uniform distribution.
Traditional slurry distribution systems typically do not provide a uniform distribution of slurry across a wafer surface. For example, most slurry distribution systems apply fresh slurry to the edge of a wafer and then transport it to the center of the wafer. However, by the time the slurry reaches the center of the wafer some of the abrasive characteristics of the slurry are spent. Thus fresh slurry applies more abrasive friction to the edge of the wafer removing material relatively fast and spent slurry applies less abrasive force to the center of the wafer removing material relatively slower resulting in an unevenly polished wafer surface.
As abrasive slurry is consumed during the polishing process waste particles comprising spent abrasive particles and waste xe2x80x9cshavedxe2x80x9d from the wafer are produced. Particulate contamination associated with spent abrasive particles can have very detrimental impacts and is a great concern with respect to the surface cleanliness after CMP. Spent abrasive particles usually cannot be readily dissolved by chemical interaction. Free spent abrasive particles in the slurry tend to increase the probability that the xe2x80x9cwastexe2x80x9d particles will deposit on the wafer surface. In addition, the residue of spent abrasive particles tends to lodge in the grooves and pits of the polishing pad that are otherwise intended to assist in carrying fresh slurry to the surface of the wafer. In order to maintain the efficient delivery of fresh slurry by the polishing pad, frequent pad conditioning is required because the pits and grooves intended to carry fresh are filled up with spent abrasive slurry particles. The most common method of pad conditioning is to remove a layer of the polishing pad surface and re-texture it with new pits and grooves. Frequent conditioning of a polishing pad typically delays the polishing process and increases the rate at which polishing pads wear out.
It is desirable to have a polishing pad that does not require abrasive assistance from slurry. A typical slurry free polishing pad has a surface with abrasive characteristics such as fixed abrasive components or particles that remove a portion of top wafer layer. Although fixed abrasive polishing pads relieve abrasive slurry concerns, particulate contamination is still an issue because of limited liquid flow that is not strong enough to remove waste products from the surface of the wafer and polishing pad during the CMP processes. In addition, scratching is also an issue because the abrasive material is no longer mobile, as in a flowing slurry system and conditioning of fixed abrasive polishing pads is not easy.
What is required is a system and method that facilitates an efficient and effective manner to polish the surface of an IC wafer. The system and method should not require free floating abrasive particles nor result in undue particle contamination on the wafer surface. It should also aid conditioning processes to prepare a pad for continued use. The system and method should facilitate defect reduction (e.g., lower defect density) and cleaner CMP processes that improve reliability of integrated circuit manufacturing.
The present invention includes a fluid dispensing fixed abrasive polishing pad device and method for efficiently polishing an IC wafer. The fluid dispensing fixed abrasive polishing pad device and method of the present invention assists a CMP process to achieve efficient wafer planarization by utilizing a fixed abrasive polishing pad with fluid provided via holes in the fixed abrasive polishing pad. The present invention is able to achieve consistent removal rate and a smooth polished wafer surface without suffering from detrimental side affects caused by abrasive slurry particles. For example, uneven layer removal due to agglomeration of the abrasive slurry particles, abrasive slurry particulate contamination deposited on the wafer surface, spent abrasive particles lodging in the grooves and pits of the polishing pad that are otherwise intended to assist in carrying fresh slurry to the surface of the wafer.
In one embodiment of the present invention, a fluid dispensing fixed abrasive polishing pad comprises a polishing pad body with fixed abrasive components and fluid dispensing ducts. The fixed abrasive component removes a portion or entire wafer layer when rubbed against the surface of the wafer without the assistance of abrasive particles suspended in a slurry, and therefore does not suffer detrimental side affects associated with abrasive slurries . The fluid dispensing duct permits fluid to flow from a surface of fluid dispensing fixed abrasive polishing pad to the wafer. The fluid dispensing fixed abrasive polishing pad is capable of dispensing a variety of fluids, including fluids comprising chemicals that assist with the polishing process and/or waste particle removal. In addition, the flow of fluid in the present invention is strong enough to remove the waste (e.g., reaction products, wafer shavings, particulate contaminants, etc.) from the surface of the wafer and the fixed abrasive polishing pad during the polishing process. In one embodiment of the fluid dispensing fixed abrasive polishing pad waste particles are sucked or vacuumed back through the fluid dispensing duct.